Achieving maximal tumor removal with minimal collateral damage to healthy tissue is a challenge in tumor surgery, because there are no reliable visual cues to indicate completeness of resection. In contrast, on a microscopic level, the differences between tumor and non-infiltrated tissues are clear. However, traditional histopathologic techniques require that the tissue be removed from the operative field, processed, and stained. Therefore, histopathology can neither be performed in situ nor in real-time. Suboptimal surgical results are extremely common in brain cancer surgery (64,000 US cases/year). Tumor that could have been safely removed has been identified in the operative cavity in 76% of cases, by post-operative MRI. In most cases, tumor recurrence occurs near the resection cavity. An in vivo technique for real-time imaging of the resection margins at the time of surgery would be highly desirable. Stimulated Raman Scattering (SRS) microscopy combines the advantages of morphological and chemical imaging of traditional histology but without requiring tissue removal or dye staining. It can thus be used in situ and in real- time. Mapping of a 2x2cm2 area can be achieved in approximately 2.5min and has the potential to provide quantitative clinical endpoints for brain tumor surgery. The accuracy of tumor detection in an animal model of glioblastoma with a state-of-the-art research-type SRS microscope has been shown to be comparable to traditional H&E microscopy, without requiring tissue removal or staining. However, there is no system that meets all the requirements for clinical SRS imaging. The present proposal is to develop a handheld SRS endoscope that is suited for use in a surgical cavity and achieves diagnostically relevant image quality and imaging speed. The goal of Phase 1 is to obtain proof-of-concept by leveraging established technologies, to the largest degree possible. None of the components have been designed for the purpose of SRS endoscopy but should be able to be modified to work for that purpose, with predictable limitations. If Phase 1 proof-of-concept is achieved, custom components would be designed in Phase 2 to improve image quality and speed. The PI has assembled a multidisciplinary team of academic, industrial and clinical thought leaders for laser engineering, miniaturized scanner development, optical design, and clinical validation. The specific aims are to (1) develop an all-fiber scanning fiber SRS endoscope and (2) rigorously demonstrate that the SRS endoscope produces diagnostically relevant image quality.